Although our understanding of the acoustic correlates of affective
state in humans is largely restricted to studies of trained actors,research
carried out in more natural settings reveals that systematic changes in
call morphology arise in response to changes in emotional state (Scherer
1986;Scherer and Kappas 1988).To contribute to the comparative liter-
ature,we have begun to look at more subtle changes in the acoustic struc-
ture of rhesus calls (in contrast to call rate) at the time of feeding.
Figure 6.2 illustrates two common situations.Early in the morning,
the rhesus began moving toward the feeding corrals.When personnel
arrived,individuals began cooing,apparently in anticipation of the chow.
It is my impression that these coos were produced with minimal vocal
effort.They tended to be relatively low in amplitude and the funda-
mental frequency contour is flat.When personnel moved toward the
feeding corrals and began putting the chow into dispensers,the coo’s
morphology was transformed.In particular,individuals appeared to put
greater effort into the call.Based on spectrographic analyses,this change
in production mode appears to cause increased vocal turbulence or
noise.In the upper panel of figure 6.2,the first coo was produced while
sitting outside the dispenser.There was virtually no noise between the
harmonics.In the second coo,noise disrupted the harmonic structure for
a brief period of time.By the final coo,the harmonic structure was almost
completely disrupted.Such acoustic changes are clearly perceptible to
the human ear and thus,presumably,to the rhesus ear as well.
In the second panel of figure 6.2,an adult male saw some coconut at
a distance and approached.The first three calls,given before and during
the approach to coconut,were coos.As the male grabbed and then ate81 Primate Vocalizations in Emotion and Thought
Figure 6.1
The relationship between rate (number of calls/minute) of food-associated calls by rhesus
monkeys and latency (minutes) to arrive and feed at the chow dispensers.Fig.6.1